The invention relates to the control of oil and gas wells using a plunger lift device and more particularly to methods for adjusting the close times and afterflow times used by a plunger lift system.
A plunger lift is an artificial lift method that is used to remove fluids from a gas well. A plunger lift system uses a freely moving plunger in the production tubing where the plunger forms a seal with the production tubing to prevent fluid from passing between the plunger and the wall of the production tubing. The plunger starts at the bottom of the well and when there is sufficient pressure behind the plunger, the plunger can be forced by this pressure to the top of the well. Fluid that has accumulated above the plunger is pushed ahead of the plunger where it is removed from the well.
The movement of the plunger is controlled by opening and closing a valve between the production tubing and an outlet line (commonly called a sales line). When the valve is closed, the plunger can drop to the bottom of the well. With the valve closed, the pressure from the well builds up and when a desired pressure level is reached, the valve can be opened connecting the production tubing with the outlet line. Because the outlet line is typically of a lower pressure than the elevated pressure in the production tubing, the gas with its elevated pressure exits through the open valve and into the outlet line. This causes the plunger to rise in the production well and up into the well head. This plunger can then be held in the well head until the gas exiting the production well through the open valve is sufficiently reduced and the plunger can then fall back down the production tubing.
Plunger lift systems can be used to produce either gas from a well or oil (or some other saleable liquid). When the plunger lift system is used to produce gas from the well, the plunger is used to remove water that has entered the well. The plunger is held at the top of the well to allow gas to flow out of the well and into the outlet line. Periodically, the plunger is dropped to the bottom of the well and then allowed to rise up the well again to carry water up and out of the well. When the plunger lift system is used to produce oil from the well, the plunger is used to produce the oil from the well and the gas is simply used to lift the plunger up the well. The plunger is allowed to fall to the bottom of the well and oil to flow into the well above the plunger. When the valve is opened and the plunger is allowed to rise up the well, the plunger will carry the oil that has accumulated on top of the plunger up to the top of the well where it can be removed.
The times used by the plunger system when the valve is opened and when the valve is closed are very important to the operation of the plunger lift system. While these times can be initially set based on an educated guess, it is very hard for a person to determine just what these times should be for a specific well and the conditions in any given well can vary from what an experienced well operator was expecting. After the initial times are determined and set, these times often need fine tuning and changing during the operation of the well in order to optimize them for a particular well. Additionally, the conditions of a well can vary over time, causing times that might have worked well with the plunger lift system at one time to not work as well over the entire time the plunger lift system is operating.